Analyse non linéaire par éléments finis du genou humain sous charges complexes en flexion

A detailed 3-D model of the tibio-femoral joint, constituted of two bony structures (tibia, femur) and their articular cartilages, the menisci and four main ligaments (two cruciate, two collateral) was developed to study the global response of the passive human knee in flexion-extension with or without external loads. Based on a validated model of the human knee joint reconstructed by Bendjaballah in 1996 from the right knee of a 27 year old female donor, this refined model has been intensely employed to perform a non-linear elastostatic analysis in passive flexion-extension in order to identify the mechanism of load transfer on the passive components of the knee under different external loads. The role of some parameters of the joint, for example, changes in initial deformations in the ligaments or rupture of a ligament, in the biomechanics of the knee was also investigated. In the current work adequate boundary conditions were used to prevent erroneous displacement computations and undesired (additional) loads while allowing for the fully unconstrained response of the joint. These boundary conditions were also altered to further study the role that they play in the global response of the knee joint.

The rigid bodies were utilised to simulate the bone structures (femur and tibia) in the current study. The articular cartilage layers were represented by solid elements. For meniscal tissue, a non-homogeneous composite model of an isotropic matrix of ground substance reinforced by a network of radial and circumferential collagen fibres was considered. Moreover, non-linear spring elements were considered to model various ligaments of the tibio-femoral joint. To take into account the wrapping of the medial collateral ligament around the proximal medial bony edge of the tibia, the wrapping elements were considered for the distal part attaching the meniscus to the tibia and wrapping over the tibia. Articulations at the cartilage-cartilage (i.e., at uncovered areas) as well as cartilage-meniscus (i.e., at covered areas) were simulated in this work as large displacement with frictionless contact. Each meniscus, simultaneously, articulated with the tibial and femoral cartilage layers at its distal and proximal surfaces, respectively. The patella was not taken into account in the present model.

During the passive flexion, the tibia rotated internally as the femur flexed whereas it rotated externally as the femur extended. A remarkable coupling was predicted between ACL and PCL forces (or initial strains); forces in both cruciates increased as the initial strain in one of them increased. (Abstract shortened by UMI.)